[RFC v2 07/26] mm/asi: Add ASI page-table entry set functions

[Alexandre Chartre]

Add wrappers around the page table entry (pgd/p4d/pud/pmd) set
functions which check that an existing entry is not being
overwritten.

Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
 arch/x86/mm/asi_pagetable.c |  124 +++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 124 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/asi_pagetable.c b/arch/x86/mm/asi_pagetable.c
index 0fc6d59..e17af9e 100644
--- a/arch/x86/mm/asi_pagetable.c
+++ b/arch/x86/mm/asi_pagetable.c
@@ -270,3 +270,127 @@ static bool asi_valid_offset(struct asi *asi, void *offset)
 
 	return p4d;
 }
+
+/*
+ * asi_set_pXX() functions are equivalent to kernel set_pXX() functions
+ * but, in addition, they ensure that they are not overwriting an already
+ * existing reference in the page table. Otherwise an error is returned.
+ */
+static int asi_set_pte(struct asi *asi, pte_t *pte, pte_t pte_value)
+{
+#ifdef DEBUG
+	/*
+	 * The pte pointer should come from asi_pte_alloc() or asi_pte_offset()
+	 * both of which check if the pointer is in the kernel isolation page
+	 * table. So this is a paranoid check to ensure the pointer is really
+	 * in the kernel page table.
+	 */
+	if (!asi_valid_offset(asi, pte)) {
+		pr_err("ASI %p: PTE %px not found\n", asi, pte);
+		return -EINVAL;
+	}
+#endif
+	set_pte(pte, pte_value);
+
+	return 0;
+}
+
+static int asi_set_pmd(struct asi *asi, pmd_t *pmd, pmd_t pmd_value)
+{
+#ifdef DEBUG
+	/*
+	 * The pmd pointer should come from asi_pmd_alloc() or asi_pmd_offset()
+	 * both of which check if the pointer is in the kernel isolation page
+	 * table. So this is a paranoid check to ensure the pointer is really
+	 * in the kernel page table.
+	 */
+	if (!asi_valid_offset(asi, pmd)) {
+		pr_err("ASI %p: PMD %px not found\n", asi, pmd);
+		return -EINVAL;
+	}
+#endif
+	if (pmd_val(*pmd) == pmd_val(pmd_value))
+		return 0;
+
+	if (!pmd_none(*pmd)) {
+		pr_err("ASI %p: PMD %px overwriting %lx with %lx\n",
+		       asi, pmd, pmd_val(*pmd), pmd_val(pmd_value));
+		return -EBUSY;
+	}
+
+	set_pmd(pmd, pmd_value);
+
+	return 0;
+}
+
+static int asi_set_pud(struct asi *asi, pud_t *pud, pud_t pud_value)
+{
+#ifdef DEBUG
+	/*
+	 * The pud pointer should come from asi_pud_alloc() or asi_pud_offset()
+	 * both of which check if the pointer is in the kernel isolation page
+	 * table. So this is a paranoid check to ensure the pointer is really
+	 * in the kernel page table.
+	 */
+	if (!asi_valid_offset(asi, pud)) {
+		pr_err("ASI %p: PUD %px not found\n", asi, pud);
+		return -EINVAL;
+	}
+#endif
+	if (pud_val(*pud) == pud_val(pud_value))
+		return 0;
+
+	if (!pud_none(*pud)) {
+		pr_err("ASI %p: PUD %px overwriting %lx with %lx\n",
+		       asi, pud, pud_val(*pud), pud_val(pud_value));
+		return -EBUSY;
+	}
+
+	set_pud(pud, pud_value);
+
+	return 0;
+}
+
+static int asi_set_p4d(struct asi *asi, p4d_t *p4d, p4d_t p4d_value)
+{
+#ifdef DEBUG
+	/*
+	 * The p4d pointer should come from asi_p4d_alloc() or asi_p4d_offset()
+	 * both of which check if the pointer is in the kernel isolation page
+	 * table. So this is a paranoid check to ensure the pointer is really
+	 * in the kernel page table.
+	 */
+	if (!asi_valid_offset(asi, p4d)) {
+		pr_err("ASI %p: P4D %px not found\n", asi, p4d);
+		return -EINVAL;
+	}
+#endif
+	if (p4d_val(*p4d) == p4d_val(p4d_value))
+		return 0;
+
+	if (!p4d_none(*p4d)) {
+		pr_err("ASI %p: P4D %px overwriting %lx with %lx\n",
+		       asi, p4d, p4d_val(*p4d), p4d_val(p4d_value));
+		return -EBUSY;
+	}
+
+	set_p4d(p4d, p4d_value);
+
+	return 0;
+}
+
+static int asi_set_pgd(struct asi *asi, pgd_t *pgd, pgd_t pgd_value)
+{
+	if (pgd_val(*pgd) == pgd_val(pgd_value))
+		return 0;
+
+	if (!pgd_none(*pgd)) {
+		pr_err("ASI %p: PGD %px overwriting %lx with %lx\n",
+		       asi, pgd, pgd_val(*pgd), pgd_val(pgd_value));
+		return -EBUSY;
+	}
+
+	set_pgd(pgd, pgd_value);
+
+	return 0;
+}
-- 
1.7.1